In recent years, hybrid vehicles and electric vehicles are receiving attention as environment-friendly vehicles. A hybrid vehicle includes as its motive power source, in addition to a conventional engine, a DC (Direct Current) power supply, an inverter, and a motor driven by the inverter. Specifically, the vehicle is powered by driving the engine, as well as by converting a DC voltage from the DC power supply into an AC (Alternating Current) voltage by the inverter so that the converted AC voltage is used to drive the motor.
An electric vehicle is powered by a DC power supply, and inverter and a motor driven by the inverter.
Generally, in such hybrid vehicle and electric vehicle, a motor current actually supplied from the inverter to the motor is detected using a current sensor, and control is exerted so that a current detect value output from the current sensor and a current specify value calculated from the required torque agrees with each other. In other words, what is called feedback control is exerted.
Herein, if a current sensor is abnormal, the current detect value output from the current sensor does not agree with the actual motor current. For example, it may be extremely smaller than the actual motor current. If the aforementioned feedback control is exerted in such a case, the actual motor current would be extremely greater than the desired current specify value. When this overcurrent passes through the inverter, a load corresponding to the magnitude of the current and the time during which the current passes is placed on the inverter, whereby the inverter may be damaged. Accordingly, in order to prevent the damage of the inverter, the abnormality of the current sensor must be detected quickly and surely.
For example, Japanese Patent Laying-Open No. 08-172721 discloses an apparatus for detecting an abnormality of a motor output system that can detect an abnormality of a system for outputting a current to a motor (hereinafter also referred to as motor current output system) so that the damage of peripheral equipment by overcurrent is prevented. Specifically, the apparatus for detecting an abnormality of a motor output system includes: a current sensor detecting an actual current passing through the motor and outputting the magnitude of the actual current as a current detect value; current compare means for constantly comparing a current specify value and the current detect value and outputting a deviation of the current detect value from the current specify value; abnormality determine means for determining that the motor current output system is abnormal when the state where the deviation being greater than a prescribed threshold value continues for at least a prescribed period; and abnormality process means for stopping the power supply to the motor when the abnormality is determined by the abnormality determine means.
With such a configuration, as the abnormality of the motor output system is determined when the state where the deviation being greater than a prescribed threshold value continues for at least a prescribed period, erroneous abnormality determination is prevented in such a case that the deviation temporarily increases due to the rise of the actual current delaying from the current specify value in a transient state or due to noises being mixed. Thus, the abnormality of the motor output system can accurately be detected and damage or the like of peripheral equipment due to supply of the overcurrent can be prevented.
However, with this conventional abnormality detecting apparatus, in consideration of preventing erroneous detection, lapse of a certain period is always necessary for determining an abnormality. When the motor current becomes an overcurrent when the motor output system is abnormal, the load placed on the inverter becomes considerably great proportionally to the certain period, and whereby the inverter may be damaged.
Further, according to the conventional abnormality detecting apparatus, when the current compare means outputs the deviation of the current detect value from the current specify value, an output waveform of the deviation between them is represented by a half wave as in FIG. 12, since the actual current and the current specify value are both sine waves inherently as shown in the figure. Thus, it cannot be compared with a prescribed threshold value in magnitude accurately. Therefore, the current compare means is configured to include a filter circuit, so that the deviation can be filtered to be converted into an output waveform represented by an alternating dot and dashed line in the figure. The converted deviation is compared with a prescribed threshold value to determine an abnormality.
On the other hand, with the current compare means with such a configuration, the outputted deviation delays by the time constant of the filter circuit. This increases the period required for determining an abnormality and the load to the inverter.